GIS is ... Geographic Information Systems

GIS are modern geoinformation mobile systems that have the ability to display their location on a map. This important property is based on the use of two technologies: geo-information and global positioning. If the mobile device has a built-in GPS receiver, then with this device it is possible to determine its location and, therefore, the exact coordinates of the GIS itself. Unfortunately, geoinformation technologies and systems in the Russian-language scientific literature are represented by a small number of publications, as a result, there is almost no information on the algorithms underlying their functional capabilities.

Classification of GIS

The subdivision of geoinformation systems is based on the territorial principle:

1. Global GIS is used to prevent man-made and natural disasters since 1997. Thanks to these data, it is possible in a relatively short time to forecast the scale of the disaster, draw up a plan for the elimination of consequences, assess the damage caused and human losses, and organize humanitarian actions.
2. The regional geoinformation system is developed at the municipal level. It allows local authorities to predict the development of a certain region. This system reflects almost all important spheres, for example, investment, property, navigation and information, legal, etc. It is also worth noting that thanks to the use of these technologies, it became possible to act as a guarantor of the safety of the life of the entire population. The regional geoinformation system is currently being used quite effectively, facilitating the attraction of investments and the rapid growth of the region's economy.

Each of the groups described above has certain subspecies:

• The global GIS includes national and subcontinental systems, usually with state status.
• In the regional - local, sub-regional, local.

Information about these information systems can be found in special sections of the network, which are called geoportals. They are placed in the public domain for review without any restrictions.

Principle of operation

Geographic information systems work on the principle of compiling and developing an algorithm. It allows you to display the movement of an object on a GIS map, including moving a mobile device within the local system. To represent a given point in a terrain drawing, you need to know at least two coordinates - X and Y. When displaying the movement of an object on the map, you will need to determine the sequence of coordinates (Xk and Yk). Their indicators should correspond to different time points of the local GIS system. This is the basis for determining the location of the object.

This sequence of coordinates can be extracted from the standard NMEA-file of GPS-receiver, which carried out real movement on the ground. Thus, the basis of the algorithm considered here is the use of NMEA-file data with coordinates of the object trajectory over a certain territory. The necessary data can also be obtained as a result of modeling the process of motion on the basis of computer experiments.

GIS Algorithms

Geoinformation systems are built on the initial data, which are taken to develop the algorithm. Typically, this is a set of coordinates (Xk and Yk) corresponding to some trajectory of the object in the form of a NMEA file and a digital GIS map on the selected terrain site. The task is to develop an algorithm that reflects the motion of a point object. In the course of this paper, we analyzed three algorithms underlying the solution of the problem.

• The first GIS algorithm is the analysis of NMEA-file data in order to extract a sequence of coordinates (Xk and Yk) from it,
• The second algorithm is used to calculate the object's angle of travel, while the parameter reading is performed from the direction to the east.
• The third algorithm is to determine the course of an object relative to the countries of the world.

Generalized algorithm: general concept

A generalized algorithm for mapping the motion of a point object on a GIS map includes the three algorithms listed above:

• Analysis of NMEA data;
• Calculation of the object's angle of travel;
• Determining the course of an object relative to countries around the globe.

Geographic information systems with a generalized algorithm are equipped with a basic control element - Timer. Its standard task is that it allows the program to generate events at regular intervals. With the help of such an object, you can set the required period for performing a set of procedures or functions. For example, for a countdown of a time interval of one second, you must set the following timer properties:

• Timer.Interval = 1000;
• Timer.Enabled = True.

As a result, every second the procedure for reading the coordinates X, Y of the object from the NMEA-file will be launched, as a result of which this point with the received coordinates is displayed on the GIS map.

How the timer works

The use of geoinformation systems is as follows:

1. Three points are marked on the digital map (symbol - 1, 2, 3), which correspond to the trajectory of the object at different times tk2, tk1, tk. They are necessarily connected by a solid line.
2. The timer that controls the movement of an object on the map can be switched on and off by means of buttons that are pressed by the user. Their meaning and a certain combination can be studied according to the scheme.

NMEA file

Let us briefly describe the composition of the NMEA GIS file. This is a document recorded in ASCII format. In fact, it is a protocol for exchanging information between a GPS receiver and other devices, such as a PC or PDA. Each NMEA message starts with a $ sign followed by a two-character device designation (for a GPS receiver - GP) and ends with the sequence \ r \ n - carriage return symbol and a newline. The accuracy of the data in the notification depends on the type of message. All information is contained in one line, with fields separated by commas.

In order to understand how geoinformation systems work, it is enough to study a widely used message such as $ GPRMC, which contains a minimal but basic data set: the location of the object, its speed and time.
Let's consider on a certain example, what information in it is coded:

• Date of determining the coordinates of the facility - January 7, 2015;
• Universal UTC time of determination of coordinates - 10h 54m 52s;
• Coordinates of the object - 55 ° 22.4271 'N And 36 ° 44.1610 'E.

We emphasize that the coordinates of the object are presented in degrees and minutes, the last figure being given with an accuracy of four decimal places (or a dot as a separator of the integer and fractional parts of the real number in the USA format). In the future, it will be necessary that in the NMEA file the latitude of the location of the object is in the position after the third comma, and the longitude - after the fifth. At the end of the message, the checksum is transmitted after the '*' symbol in the form of two hexadecimal digits - 6C.

Geoinformation systems: examples of compiling an algorithm

Consider an analysis algorithm for the NMEA file to retrieve a set of coordinates (X and Yk) corresponding to the object's motion path . It is composed of several successive steps.

Determination of the coordinate Y of the object

NMEA Data Analysis Algorithm

Step 1. Read the GPRMC line from the NMEA file.

Step 2. Find the position of the third comma in the line (q).

Step 3. Find the position of the fourth comma in the line (r).

Step 4. Find the decimal point symbol (t) starting at position q.

Step 5. Extract one character from the line in the position (r + 1).

Step 6. If this character is W, then the NorthernHemisphere variable is set to 1, otherwise -1.

Step 7. Extract (r- + 2) characters of the line starting at position (t-2).

Step 8. Extract (tq-3) the characters of the string starting at position (q + 1).

Step 9. Convert strings to real numbers and calculate the Y coordinate of the object in a radian measure.

Determination of the X coordinate of the object

Step 10. Find the position of the fifth comma in the line (n).

Step 11. Find the position of the sixth comma in the line (m).

Step 12. Find the decimal point symbol (p) starting at position n.

Step 13. Extract one character from the line in the position (m + 1).

Step 14. If this character is equal to 'E', then the variable EasternHemisphere gets the value 1, otherwise -1.

Step 15. Extract (m-p + 2) character string starting at position (p-2).

Step 16. Extract (p-n + 2) characters of the line starting at position (n + 1).

Step 17. Convert strings to real numbers and calculate the X coordinate of the object in a radian measure.

Step 18. If the NMEA file is not read through, go to step 1, otherwise go to step 19.

Step 19 Finish the algorithm.

In steps 6 and 16 of this algorithm, NorthernHemisphere and EasternHemisphere variables are used to numerically encode the location of an object on the Earth. In the northern (southern) hemisphere, the variable NorthernHemisphere takes the value 1 (-1), respectively, similarly in the eastern (western) hemisphere EasternHemisphere - 1 (-1).

Application of GIS

The use of geoinformation systems is widespread in many areas:

• Geology and cartography;
• Trade and services;
• Cadastre;
• Economy and management;
• Defense;
• Engineering;
• Education, etc.